Electrical fuse device based on a phase-change memory element and corresponding programming method

ABSTRACT

A fuse device has a fuse element provided with a first terminal and a second terminal and an electrically breakable region, which is arranged between the first terminal and the second terminal and is configured to undergo breaking as a result of the supply of a programming electrical quantity, thus electrically separating the first terminal from the second terminal. The electrically breakable region is of a phase-change material, in particular a calcogenic material, for example GST.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrical fuse device based on aphase-change memory element and to a corresponding programming method,in particular for a read-only memory (ROM) of the one-time-programmable(OTP) type, to which the following description will make reference,without this implying any loss in generality.

2. Description of the Related Art

As is known, in the manufacturing process of integrated circuits,one-time-programmable ROMs find a wide range of applications forpermanent storage of information, or for forming permanent connectionswithin integrated circuits. For example, these memories can be used forprogramming redundant elements in order to replace identical elementsthat have proven faulty during an electrical testing (operation known asEWS—Electrical Wafer Sorting), prior to carrying out packaging orsoldering of the integrated circuits on the board, or else for storageof basic information regarding the integrated circuit, such asidentifier codes or calibration information. In particular, theaforesaid information must be stored in a permanent way in order to berecovered after the packaging or soldering operations.

In order to produce the aforesaid memories using semiconductortechnology, the use of E²PROM (Electrically Erasable ProgrammableRead-Only Memory) devices, fuse devices and anti-fuse devices has beenproposed. However, for reasons that will be briefly set forth, thesolutions referred to have some problems that do not make their usetotally satisfactory within modern integrated devices.

In particular, E²PROM devices require oxide layers having a largethickness (for example, 7 nm) to prevent high leakage currents andsustain a charge stored on a corresponding floating terminal. The scalesof integration required by modern integrated circuits do not alwaysenable use of such large oxide thicknesses. Furthermore, the use ofE²PROM devices in any case involves a high area occupation.

The fuse devices commonly used for the applications referred to aboveare programmed using a laser, which is used to cut a connection afterthe fuse device has been manufactured. Laser programming entails anadditional process step, extraneous to semiconductor technology, andmoreover calls for a perfect alignment of the laser with respect to thefuse device to be programmed.

Anti-fuse devices are typically based on the perforation ofmetal-insulator-metal structures to obtain low-resistance paths. Saiddevices require high programming voltages, and consequently involve highbreaking voltages of the programming circuits associated thereto.Furthermore, said devices are generally of a horizontal type and involvea high area occupation.

Other types of semiconductor fuse devices that can be electricallyaltered, for example based on polysilicon resistors, have been proposed,for example in the U.S. Pat. No. 6,337,507 and in the patent applicationNo. US 2003/0218492. However, none of said devices is optimized in termsof costs, manufacturing times, and programming times (which should be asshort as possible).

Phase-change memories (PCMs) are moreover known, which exploit, forstorage of information, the characteristics of materials that have theproperty of switching between phases having different electricalcharacteristics. For example, said materials can switch between adisorderly, amorphous phase and an orderly, crystalline orpolycrystalline phase, and the two phases are associated toresistivities having considerably different values, and consequently todifferent values of a stored datum. Currently, the elements of Group VIof the periodic table, such as tellurium (Te), selenium (Se), orantimony (Sb), referred to as calcogenides or calcogenic materials, mayadvantageously be used to obtain phase-change memory cells. Thecurrently most promising calcogenide is formed by an alloy of Ge, Sb andTe, generically referred to as GST (for example, Ge₂Sb₂Te₅).

The phase changes are obtained by locally increasing the temperature ofthe cells of calcogenic material by means of resistive electrodes(generally known as heaters) set in contact with the region ofcalcogenic material. A selection device (for example, a MOSFET or abipolar transistor), is connected to the heater and is configured toenable passage of a programming electrical current through the heater.Said electrical current, by the Joule effect, generates the temperaturesnecessary for phase change. In particular, since the minimization of thearea of contact between the heater and the region of calcogenic materialis a primary requisite in such devices, in order to ensure repeatabilityof the programming operations, the heaters generally havesublithographic sections (i.e., dimensions smaller than the dimensionsthat can be achieved with current lithographic techniques, for examplesmaller than 100 nm, down to approximately 5-20 nm).

A wide range of manufacturing processes have been proposed to obtainphase-change memory cells, and the configurations of the resultingmemory cells are different, in particular as regards coupling betweenthe heater and a corresponding calcogenic region. For example, amicrotrench architecture is described in U.S. Pat. No. 6,891,747, whilea lance-shaped or ring-shaped tubular architecture is described in U.S.patent application Ser. No. 11/398,858, filed on Apr. 6, 2006.

Although advantageous as regards performance and manufacturing costs,PCMs cannot be used in the applications described above. In fact, thehigh temperatures that are generated during the processes of packagingor soldering on the board can lead to the change of state of previouslyprogrammed memory cells and the consequent loss of the storedinformation. In particular, the possibility exists that memory cells inthe amorphous state will switch to the crystalline state on account ofsaid high temperatures.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present invention is a fuse device (in particularfor one-time-programmable memory elements) that enables the aforesaiddisadvantages and problems to be overcome.

According to one embodiment of the present invention, a fuse deviceincludes a fuse element having a first terminal and a second terminal,and an electrically breakable region arranged between said first andsecond terminals and configured to undergo breaking as a result of thesupply of a programming electrical quantity, wherein said electricallybreakable region comprises phase-change material.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present invention, preferredembodiments thereof are now described, purely by way of non-limitingexample and with reference to the attached plate of drawings, wherein:

FIG. 1 is a schematic top plan view of a semiconductor fuse deviceaccording to a first embodiment of the present invention, with partsremoved for greater clarity;

FIG. 2 is a cross-sectional view of a portion of the fuse device of FIG.1 taken along the line II-II, in which a phase-change fuse element isillustrated, in a first operating condition;

FIG. 3 is a view similar to that of FIG. 2 regarding a second operatingcondition of the phase-change fuse element;

FIGS. 4-6 show graphs regarding electrical quantities associated to thefuse element of FIGS. 2 and 3;

FIG. 7 is a view similar to that of FIG. 1, illustrating a variant ofthe fuse device;

FIG. 8 is a view similar to that of FIG. 7, illustrating a furthervariant of the fuse device;

FIG. 9 is a top-plan view of a second embodiment of the fuse device; and

FIG. 10 is a cross-sectional view of the fuse device of FIG. 9, takenalong the line X-X;

FIG. 11 is a top-plan view of a third embodiment of the fuse device;

FIG. 12 shows a cross-sectional view of the fuse device of FIG. 11,taken along the line XII-XII;

FIG. 13 is a top-plan view of a fourth embodiment of the fuse device;

FIG. 14 shows a cross-sectional view of the fuse device of FIG. 13,taken along the line XIV-XIV; and

FIG. 15 shows a simplified block diagram of a one-time-programmablestorage device.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention envisages use of a phase-changememory element to provide a semiconductor fuse device. The phase-changememory element is programmed for this purpose in two stable states: alow-resistivity closed state (for example corresponding to a “1”), andan open state (for example corresponding to a “0”). In particular, theopen state is obtained by physical breaking of a region of calcogenicmaterial of the phase-change memory element, via application of a givenelectrical quantity (in particular, via the passage of a high electricalcurrent). In this manner, the information associated to both states arestable and not modifiable, for example by soldering or packaging of acorresponding integrated circuit.

In detail, and as illustrated in FIGS. 1 and 2, a fuse device 1according to a first embodiment of the present invention, comprises afuse element 2 (as will be clarified hereinafter, based on aphase-change memory element), and a selector element 3, which iselectrically connected to the fuse element 2 and is configured to enableprogramming of the fuse element 2. In particular, by way of example, theselector element 3 illustrated in FIG. 1 is an N-channel MOSFET of aplanar type. It is clear, however, that other selector elements could beused in an altogether equivalent way, for example any FET (verticalMOSFET, JFET, FinFET, etc.), or else a BJT or a BiFET. Furthermore, FIG.1 and the following figures illustrate a phase-change memory elementhaving a microtrench architecture. Once again, it is clear that otherstructures could be used in an altogether equivalent way, for example ofthe wall or tubular type.

In detail, the selector element 3 is provided with: a firstcurrent-conduction region (in particular, a current-input region), inthe example a drain region 4, and a second current-conduction region (inparticular, a current-output region), in the example a source region 5,which are formed, in a known way, within a substrate 6 of semiconductormaterial (in particular silicon); and a control region, in the example,a gate region 7, set above the substrate 6 between the drain region 4and source region 5, and partially overlapping them. The aforesaidregions are coated with a respective silicidation region 8, and contactelements 9 a, 9 b, in particular plugs, made, for example, of tungstensurrounded by a Ti/TiN multilayer, extend vertically with respect to thesubstrate 6, from the drain region 4 and the source region 5,respectively.

As illustrated in detail in FIG. 2, the fuse element 2 has a verticalstructure and comprises a bottom electrode 10, made, for example, oftungsten (W), surrounded by first barrier regions 11, for exampleconstituted by a Ti/TiN multilayer. In particular, the bottom electrode10 is made by an end portion of a contact element 9 a associated to thedrain region 4 of the selector element 3, preferably a contact elementarranged in a central position with respect to the drain region 4 sothat the fuse element 2 is set above the drain region.

A heater 12 is placed on, and in contact with, the bottom electrode 10.The heater 12, as may be seen in FIG. 1, extends along the periphery ofan approximately rectangular area, and has a first long portion 12 a anda second long portion 12 b, and a first short portion 12 c and a secondshort portion 12 d, said long portions and short portions beingorthogonal to one another. Each of said portions 12 a-12 d (asillustrated for example in the next FIG. 10) has a channel-shapedstructure, and is made by a metallic coating, for example of TiSiN,which forms respective side walls and a respective bottom surface, andby a dielectric filling material. Contact between the bottom electrode10 and the bottom wall of the heater 12 occurs at a central area of thefirst long portion 12 a of the heater 12. The second long portion 12 bis instead set outside the drain region 5.

A phase-change memory element 13 (referred to in what follows as PCMelement 13) is set above the heater 12, in particular above the firstlong portion 12 a thereof, in a position vertically corresponding to thebottom electrode 10. In detail, the PCM element 13 comprises acalcogenic region 15, made of phase-change material, for example GST(Ge₂Sb₂Te₅), and a second barrier region, made, for example, of Ti/TiN,on the calcogenic region 15. In particular, the second barrier regionconstitutes a top electrode 16 of the fuse element 2. The PCM element 13extends longitudinally on an approximately rectangular area(approximately parallel to the first and second short portions 12 c, 12d of the heating element 12) crossing the long portion 12 a of theheating element 12. Moreover, the PCM element 13 is formed (in a knownway) with the microtrench technique, and the calcogenic region 15contacts the walls of the central area of the first long portion 12 a ofthe heater 12 only at a central depression having a cross section withsublithographic dimensions. The area of contact is a storage area 15 a(and, as will be clarified hereinafter, an electrically breakable area)of the fuse device 1. A closing region 17, made, for example, of siliconnitride, surrounds the PCM element 13 and covers the heater 12 at thetop. In addition, an insulation region 19 surrounds and electricallyinsulates the fuse element 2.

In use, via purposely provided electrical contacts (not illustrated),the top electrode 16 is connected to a high-voltage line V_(cc), forexample to the supply line of the fuse device 1, and the source region5, via the corresponding contact elements 9 b, is connected to areference-voltage line GND of the fuse device 1. When enabled by acontrol signal supplied to the gate region 7, a programming currentconsequently passes through the fuse element 2 from the top electrode 16to the bottom electrode 10, traversing the calcogenic region 15 and thestorage area 15 a, and then flows through the selector element 3 fromthe drain region 4 to the source region 5.

According to one embodiment of the present invention, the open state ofthe fuse element 2 is programmed by applying a current and a voltagehaving a value such as to cause physical breaking of the storage area 15a. For this purpose, a programming pulse is applied having a duration,for example, of between 100 ns and 1 μs, with a current of, for example,2.5 mA, and a voltage of, for example, 2.5 V. As illustrated in FIG. 3,said programming pulse causes breaking of the storage area 15 a, andcreation of a void 20, which interrupts the electrical connectionbetween the top electrode 16 and the bottom electrode 10 of the fuseelement 2 (creating the open state, or high-resistance state). Indetail, the void 20 extends in part in the calcogenic region 15 and inpart in the heater 12. As illustrated in FIGS. 4 and 5, relating toexperimental tests conducted by the applicant with a fuse device 1 builtwith a 180-nm technology and with programming pulses of 300 ns, breakingof the storage area 15 a is obtained using voltages having a value ofbetween approximately 2 V and 3 V (preferably 2.5 V), and currentshaving a value of between approximately 2 mA and 3 mA (preferably 2.5mA).

The closed state of the fuse element 2 is instead programmed by applyingto the storage area 15 a a triangular voltage pulse (FIG. 6), forexample having a duration of 1 μs and an amplitude of 700 μA. Said pulsecauses melting of the calcogenic material (at a temperature ofapproximately 600° C.) and subsequent slow cooling thereof, which leadsto its crystallization. Alternatively, a single crystallization pulsecan be applied, or else a sequence of pulses having decreasingamplitudes. Typically, the crystallization procedure has a duration ofbetween 1 and 10 μs.

Given the high values of current used in the breaking operations of thefuse device 1, one embodiment of the present invention envisagesexploitation of the so-called “ballast” effect to prevent the knowneffects of “crowding” of the current and of thermal “run-away” of theselector element 3. In a per se known manner, the ballast effect leadsto a greater uniformity of the current distribution, and occurs as theresistance increases along the path of the current.

For the above purpose (see FIG. 7), according to a first variant, thePCM element 13 is arranged above the second long portion 12 b of theheater 12 at a distance from the contact elements 9 a associated to thedrain region 4. The electrical contact with the PCM element 13, and inparticular with the storage area 15 a, is in any case guaranteed by thepresence of metallic material on the side walls and on the bottomsurface of the heater 12, and by its continuity. However,advantageously, the heating element represents a series resistance tothe passage of the programming current.

According to a further variant (illustrated in FIG. 8), the seriesresistance in the path of the programming current, and hence theaforesaid ballast effect, can be further increased by removing thesilicidation regions 8 on the source and drain regions (thus creating anadditional series resistance on both the source and drain contacts), andpossibly moving the contact elements 9 a of the drain region 4 away fromthe gate region 7 (as indicated by the arrow in the figure).

In any case, the configuration of the fuse device 1 previously describedenvisages the passage of the programming current in the fuse element 2from the top electrode 16 to the bottom one 10. Experimental testsconducted by the applicant have, however, demonstrated an even betterrepeatability of the programming operations of the fuse element when thedirection of the flow of the programming current is reversed. For thispurpose, according to further embodiments of the present invention,alternative configurations of the fuse device 1 are proposed, whichshare the feature of envisaging a flow of the programming current fromthe bottom electrode 10 to the top electrode 16 of the fuse element 2.

A second embodiment, illustrated in FIGS. 9 and 10, envisages again theuse of a selector element 3 of the planar N-channel MOSFET type, but inthis case the bottom electrode 10 of the fuse element 2 is connected tothe source region 5 of the selector element 3.

In detail, the selector element 3 has an active area 22, having P-typeconductivity, made within the substrate 6 (having a P-doping) andisolated by means of isolation trenches 23, for example using theShallow-Trench Isolation (STI) technique. The drain region 4 and thesource region 5 are provided within the active area 22; in detail, thedrain region 4 comprises a first drain strip 4 a and a second drainstrip 4 b, which extend in a first direction x parallel to one another,and the source region 5 comprises a source strip extending in the firstdirection x between the drain strips 4 a, 4 b. In addition, electricalcontacts 24 (illustrated in FIG. 9) contact the drain strips 4 a, 4 b.The gate region 7 is constituted by a polysilicon rectangular ringstructure, which has long portions set between the drain region and thesource region, and short portions, which extend in a second direction y,orthogonal to the first direction x, and are set outside the active area22, where they are contacted by electrical gate contacts. In addition tothe fuse element 2, the fuse device 1 comprises two pairs of “dummy”elements 25, arranged laterally to the fuse element 2. Each “dummy”element has the same structure as the fuse element 2, but is notelectrically connected and is hence not crossed by current during theprogramming steps. The presence of the dummy elements 25, however,enables uniform operation of the fuse element 2.

With reference in particular to FIG. 10, a contact element 9 a,associated to the drain region 4, for example a line of tungstenextending in the first direction x, is electrically connected, via theelectrical contacts 24, to the high-voltage line V_(cc) (in a way notillustrated), while a contact element 9 b, similar to the contactelement 9 a and associated to the source region 5, is connected to theheater 12 of the fuse element 2 (thus constituting its bottom electrode10). In particular, the heater 12 has a rectangular shape, contained inthe direction y by the long portions of the gate region 7, and is againconstituted by a metallic coating 26, for example of TiSiN, formingrespective side walls and a respective bottom surface, and by adielectric filling material 27. The PCM element 13 is set above theheater 12, and has a rectangular shape extending in the second directiony, starting from a central area of the heater 12 towards the seconddrain strip 4 b, overstepping the gate region 7. Contact plugs(so-called “vias 0”) 28 electrically connect the top electrode 16 to afirst metallization 29 (level-1 metal) that runs in the second directiony over the entire active area 22. The first metallization 29 is alsoconnected to the reference-voltage line GND of the fuse device 1.

In use, the programming current flows from the supply line V_(cc) to thedrain region 4, and then to the source region 5. From the source region5 it flows to the bottom electrode 10, and then through the PCM element13 (and in particular the storage area 15 a) to the top electrode 16, upto the reference-voltage line GND. In particular, the bottom electrode10 is set at a potential higher than that of the top electrode 16, and,as desired, the current flows from the bottom electrode to the top one.

Said arrangement is therefore advantageous for improving therepeatability of the programming operations, but feels, however, thebody effect occurring in the N-channel MOSFET, due to the voltageincrease of the source region 5.

To solve the above problem, a third embodiment (FIGS. 11-12), envisagesa configuration substantially similar to the one described withreference to FIGS. 9-10, with the difference that a P-channel planarMOSFET is used for the selector element 3. In this case, the active areais constituted by a well 30 of N type within a substrate of P⁻ type, andthe drain region 4 and source region 5 are also doped with a P-typedoping. Said solution has the advantage of not feeling the body effect;however, as is known, the use of P-channel transistors, given the samearea occupation, entails the generation of currents of lower value ascompared to the use of N-channel transistors.

A fourth embodiment (illustrated in FIGS. 13-14) envisages again the useof a selector element 3 of an N-channel MOSFET type, and at the sametime enables elimination of the body effect.

In detail, the drain region 4 and the source region 5 are in this caseconstituted by respective strips extending in the first direction x, andthe gate region 7 is also constituted by a strip, which is set betweenthe source and drain regions and carries respective gate contacts at itsends, outside the active area 22.

As illustrated in detail in FIG. 14, a contact element 9 b associated tothe source region 5 is connected, via a first plug 32, for example madeof tungsten surrounded by a Ti/TiN multilayer, to a first metallization29, connected in turn to the reference-voltage line GND. A contactelement 9 a associated to the drain region 4 is instead connected, via asecond plug 34, to a second metallization 35 (constituting an internalnode). The second metallization 35 extends in the first direction x,until it reaches the top electrode 16 of the fuse element 2, to which itis connected via a third plug 36 (so-called “via 0”). The bottomelectrode of the fuse element 2 is instead connected to a connectionline 38, for example made of tungsten, provided above the substrate 6,in a position corresponding to an isolation trench 23. A fourth plug 39connects the connection line 38 (which also extends in the firstdirection x) to a third metallization 40, connected to the high-voltageline V_(cc).

In use, the programming current flows from the supply line V_(cc) to theconnection line 38 (the bottom electrode of the fuse element), thenthrough the PCM element 13 (and in particular the storage area 15 a) andthe top electrode 16; from this it flows through the secondmetallization 35 to the drain region 4, then to the source region 5, andfinally to the reference-voltage line GND. In particular, also in thiscase, the current flows advantageously from the bottom electrode 10 tothe top electrode 16.

According to said configuration, the fuse element 2 is not verticallyaligned to one of the current-conduction regions of the selector element3, as in the preceding solutions, but is shifted laterally (in thesecond direction y). Said configuration consequently entails a greaterarea occupation as compared to the preceding solutions. At the sametime, it does not feel the body effect, in so far as the source region 5is connected to the reference-voltage line GND.

As illustrated in FIG. 15, the fuse device 1 can advantageously be usedas a memory element of a one-time-programmable ROM storage device 50. Inparticular, the ROM storage device 50 comprises a bank of programmablefuses 52 comprising a plurality of fuse devices (each made as describedpreviously), and a purposely provided programming circuit 54, coupled tothe bank of programmable fuses 52 to carry out programming thereof.

The advantages of the fuse device and of the corresponding programmingmethod are clear from the foregoing description.

In any case, it is emphasized that the fuse device has reduced costs andarea occupation, and small programming times (less than 10 μs, if both“0” and “1” data are programmed; less than 100 ns if only the “0” datumis programmed, as described hereinafter). Furthermore, it does notrequire either additional process steps with respect to the classicsteps of the semiconductor industry (as, instead, is required forexample by the laser-programmed fuses), or thick oxide layers (as,instead, is required by the E²PROMs). The described structures also havea vertical structure, and a small overall encumbrance.

The electrical alteration of the fuse device is highly repeatable,thanks to the fact that the area of contact between the PCM element andthe heater has small (i.e., sublithographic) dimensions, which arecontrollable with extreme precision. Said repeatability is furtherincreased in the arrangements envisaging a flow of current in the fuseelement 2 from the bottom electrode 10 to the top electrode 16.

Amongst the various embodiments described, particularly advantageous isthe one that envisages the use of a P-channel selector transistor.

Furthermore, tests conducted by the applicant have demonstrated thecapability of the fuse device to maintain the programmed data, evenafter baking at 250° C. for 24 hours.

In addition, it is reasonable to expect that the breaking currents andvoltages will follow the same scaling law as PCM memory cells(described, for example, in “Scaling Analysis of Phase-Change MemoryTechnology”, Pirovano et al., IEDM Tech. Dig., pp. 699-702, 2003). Inparticular, the breaking voltage will remain practically constant,whilst the programming current will decrease linearly as the scale ofintegration used in the manufacturing process decreases. Advantageously,this will enable fuse devices (inclusive of the fuse element and thecorresponding selector element) to be made that are increasingly compactwith scaling-down of the technology used.

Finally, it is clear that modifications and variations can be made towhat is described and illustrated herein, without thereby departing fromthe scope of the present invention, as defined in the annexed claims.

In particular, the programming of the closed state (corresponding to the“1” value) is not strictly necessary in so far as, as is known, storageelements made of virgin calcogenic material are already crystalline(low-resistivity state), and remain crystalline even after operationssuch as on-board packaging and soldering (consequently, the informationassociated to the crystalline state is stable). However, it may beadvantageous to program, as described previously, also the closed state,to obtain higher values of conductivity (and so facilitate theoperations of reading, for example using sense amplifiers).

Finally, it is emphasized that programming of the fuse element 2 can beachieved via selector elements different from the ones illustrated (forexample using BJTs).

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

1. A fuse device, comprising: a fuse element having a first terminal; asecond terminal; a phase-change region, including an electricallybreakable region of phase-change material configured to undergo breakingas a result of the supply of a programming electrical quantity; and aheating element of conductive material in contact with said firstterminal, said electrically breakable region being arranged at a contactarea between said heating element and said phase-change region; and aselector element electrically connected to said fuse element andconfigured to enable the supply of said programming electrical quantityto said fuse element.
 2. The fuse device according to claim 1, whereinsaid phase-change material is a calcogenic material, in particular GST.3. The fuse device according to claim 1, wherein said contact area is ata bottom side of the phase-change region and the second terminalcontacts a top side of the phase-change region, the fuse device furthercomprising an electrical connection element connecting the selectorelement to the phase-change region via the second terminal.
 4. The fusedevice according to claim 1, wherein said selector element is atransistor element having a current input terminal and a current outputterminal.
 5. The fuse device according to claim 4, wherein said selectorelement is configured to enable supply to said electrically breakableregion of a programming pulse with a current comprised between 2 mA and3 mA, a voltage comprised between 2 V and 3 V, and a duration comprisedbetween 100 ns and 1 μs.
 6. The fuse device according to claim 4,wherein said heating element has a rectangular ring shape having a firstlong side and a second long side including conductive material, saidfirst long side being arranged above said selector element and saidsecond long side being spaced apart from said selector element; andwherein said electrically breakable region is in contact with saidsecond long side, and said current input terminal is connected to saidfirst long side.
 7. The fuse device according to claim 4, wherein saidfirst terminal is connected to said current output terminal, said secondterminal is connected to a first line set at a first potential, and saidcurrent input terminal is connected to a second line set at a secondpotential, higher than said first potential.
 8. The fuse deviceaccording to claim 7, wherein said selector element is a P-channelplanar MOSFET.
 9. The fuse device according to claim 4, wherein saidcurrent input terminal is connected to said second terminal, saidcurrent output terminal is connected to a first line set at a firstpotential, and said first terminal is connected to a second line set ata second potential, higher than said first potential.
 10. The fusedevice according to claim 9, wherein said selector element is formed ina substrate of semiconductor material, and said first terminal is incontact with a first connection line provided above said substrate, thefuse device further comprising: first contact elements connecting saidcurrent input terminal to a second connection line of conductivematerial; second contact elements connecting said second connection lineto said second terminal; and third contact elements connecting saidfirst connection line to said second line.
 11. The fuse device accordingto claim 1, wherein said fuse element has a vertical structure, and saidelectrically breakable region has a cross section with sublithographicdimensions.
 12. The fuse device according to claim 1, wherein, in atleast one operating condition, said first terminal has a voltage higherthan a voltage of said second terminal, and said programming electricalquantity comprises a programming current flowing from said firstterminal to said second terminal.
 13. The fuse device according to claim1, wherein the contact area is laterally spaced apart from the selectorelement.
 14. The fuse device according to claim 1, wherein the heaterelement is a vertically-arranged thin film of conductive material thatcontacts the phase-change region at the contact area, which has asublithographic dimension.
 15. A one-time-programmable storage device,comprising a plurality of fuse devices, each fuse device including: afuse element having a first terminal; a second terminal; a phase-changeregion, including an electrically breakable region of phase-changematerial configured to undergo breaking as a result of the supply of aprogramming electrical quantity; and a heating element of conductivematerial in contact with said first terminal, said electricallybreakable region being arranged at a contact area between said heatingelement and said phase-change region; and a selector elementelectrically connected to said fuse element and configured to enable thesupply of said programming electrical quantity to said fuse element. 16.The storage device according to claim 15, further comprising aprogramming circuit configured to supply to at least one of said fusedevices said programming electrical quantity.
 17. The storage deviceaccording to claim 15, wherein said contact area is at a bottom side ofthe phase-change region and the second terminal contacts a top side ofthe phase-change region, the fuse device further comprising anelectrical connection element connecting the selector element to thephase-change region via the second terminal.
 18. The storage deviceaccording to claim 15, wherein said selector element is configured toenable supply to said electrically breakable region of a programmingpulse with a current comprised between 2 mA and 3 mA, a voltagecomprised between 2 V and 3 V, and a duration comprised between 100 nsand 1 μs.
 19. The storage device according to claim 15, wherein saidselector element is a transistor element having a current input terminaland a current output terminal, and wherein said heating element has arectangular ring shape having a first long side and a second long sideincluding conductive material, said first long side being arranged abovesaid selector element and said second long side being spaced apart fromsaid selector element; and wherein said electrically breakable region isin contact with said second long side, and said current input terminalis connected to said first long side.
 20. The storage device accordingto claim 15, wherein said selector element is a P-channel planar MOSFET.21. The storage device according to claim 15, wherein said selectorelement is a transistor element having a current input terminal and acurrent output terminal, and wherein said selector element is formed ina substrate of semiconductor material, and said first terminal is incontact with a first connection line provided above said substrate, thefuse device further comprising: first contact elements connecting saidcurrent input terminal to a second connection line of conductivematerial; second contact elements connecting said second connection lineto said second terminal; and third contact elements connecting saidfirst connection line to said second line.
 22. The storage deviceaccording to claim 15, wherein said fuse element has a verticalstructure, and said electrically breakable region has a cross sectionwith sublithographic dimensions.
 23. The storage device according toclaim 15, wherein the contact area is laterally spaced apart from theselector element.
 24. A method for programming a fuse device providedwith a fuse element having a first terminal; a second terminal; aphase-change region, including an electrically breakable region ofphase-change material arranged between said first and second terminals;and a heating element of conductive material in contact with said firstterminal, said electrically breakable region being arranged at a contactarea between said heating element and said phase-change region, themethod comprising breaking said electrically breakable region, whereinbreaking said electrically breakable region comprises supplying to saidphase-change material a programming electrical quantity such as to causebreaking thereof, wherein supplying the programming electrical quantitycomprises supplying a programming current flowing between said firstterminal and said second terminal so as to form a void in saidelectrically breakable region.
 25. The method according to claim 24,wherein supplying the programming electrical quantity comprisessupplying to said electrically breakable region a programming pulse witha current comprised between 2 A and 3 A, a voltage comprised between 2 Vand 3 V, and a duration comprised between 100 ns and 1 μs.
 26. Themethod according to claim 24, wherein supplying a programming electricalquantity comprises supplying a programming current flowing from saidfirst terminal to said second terminal so as to form the void in saidelectrically breakable region.
 27. The method according to claim 24,further comprising programming said electrically breakable region in afirst low-resistivity operating condition, so as to electrically connectsaid first and second terminals, and programming said electricallybreakable region in a second high-resistivity operating condition, so asto electrically disconnect said first terminal from said secondterminal; programming in said second high-resistivity operatingcondition comprising said step of breaking said electrically breakableregion.
 28. A process for manufacturing a fuse device, comprising:forming a fuse element using steps including: forming a first terminaland a second terminal; and forming an electrically breakable regionbetween said first terminal and said second terminal, wherein formingthe electrically breakable region comprises forming a region ofphase-change material; and forming a heating element of conductivematerial in contact with said first terminal, said electricallybreakable region being arranged at a contact area between said heatingelement and said electrically breakable region; and forming a selectorelement electrically connected to said fuse element and configured toenable the supply of said programming electrical quantity to said fuseelement.
 29. The process according to claim 28, wherein said contactarea is at a bottom side of the phase-change region and the secondterminal contacts a top side of the phase-change region, the processfurther comprising forming an electrical connection element connectingthe selector element to the phase-change region via the second terminal.30. The process according to claim 28, wherein said selector element isa transistor element having a current input terminal and a currentoutput terminal, and wherein said heating element has a rectangular ringshape having a first long side and a second long side includingconductive material, the process further comprising arranging said firstlong side above said selector element and spacing apart said second longside from said selector element; and wherein said electrically breakableregion is in contact with said second long side, and said current inputterminal is connected to said first long side.
 31. The process accordingto claim 28, wherein the contact area is laterally spaced apart from theselector element.